The group B Streptococcus (GBS) is the most serious pathogen for the neonatal age group. Antibody to the capsular polysaccharides of GBS has been shown to be protective. The majority of neonatal infections are due to strains having the type III capsule. We have previously purified and defined the structure of the type III polysaccharide. The purified polysaccharide has been used as an experimental vaccine in humans with immunogenicity rates of 40- 70% in nonimmune recipients. The goals of this proposal are twofold: 1) to define the structural characteristics of the immunodeterminant of the type III polysaccharides and 2) to develop an oligosaccharide-protein conjugate vaccine in order to overcome the variable immunogeneity of the native type III polysaccharide. To accomplish these goals we have 5 specific aims. In the Specific Aim 1 of the current proposal we will chemically construct oligosaccharides between 1 and 2 repeating units (5-10 sugars) in size for defining the structure of the immunodeterminant site on the type III GBS polysaccharide. We believe this study is fundamental to a basic understanding of the interaction of polysaccharide antigens with the immune system. Specific aims 2, 3, 4, and 5 are specifically directed towards the development and testing of an oligosaccharide protein conjugate vaccine. We have prepared oligosaccharides suitable for use in a conjugate vaccine by depolymerization of the type III polysaccharide using a specific endo-beta-galactosidase. In Specific Aim 2 we will develop methods of large scale production of the oligosaccharides. This will be done by cloning the enzyme in order to enhance production. In specific Aim 3 we will couple the oligosaccharides of defined molecular sizes to protein carriers. In Specific Aim 4 we will optimize this conjugate vaccine for oligosaccharide chain length and coupling density. Finally, in Specific Aim 5 we will test the conjugate vaccine for induction of IgG, T cell dependence and functional antibody.